1. Field of the Invention
The present invention relates generally to a motor for use in a treadmill and more particularly, to an external rotor brush motor, which has the motor shell functions as the rotor as well as the inertia flywheel and, which uses a brush DC design to eliminate the arrangement of a direction change and control circuit that is requisite in a brushless motor.
2. Description of the Related Art
FIGS. 6 and 7 show an internal rotor DC motor 20 used in a treadmill 10 according to the prior art. According to this design a heavy inertia flywheel 23 is installed in the output shaft 22, which is coupled to the internal rotor 21, and a drive wheel 24 is mounted on the output shaft 22 and coupled to a driven wheel 13 through a transmission belt 25 for driving the driven wheel 13 to rotate the roller 12 and the treadmill belt 11 on which the user treads. Because the heavy inertial flywheel 23 is necessary, labor and material cost is relatively increased. Further, dynamic balance of the heavy inertial flywheel 13 and the motor 20 are separately handled, complicating precision control.
U.S. Pat. No. 6,661,136 (equivalent to Taiwan publication no. 535603), issued to the present inventor, discloses an external rotor DC motor, which saves much labor and material cost. This structure of external rotor DC motor is functional, however its low heat dissipation efficiency may affect high performance of the motor. Further, because the controller of this design of external rotor DC motor is expensive, this structure of brushless external rotor DC motor is not practical for use in a treadmill of relatively low price.
Therefore, it is desirable to provide an external rotor brush DC motor that eliminates the aforesaid drawbacks.
The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide an external rotor brush DC motor, which dissipates heat quickly during operation, thereby achieving high performance. It is another object of the present invention to provide an external rotor brush DC motor, which is durable in use. It is still another object of the present invention to provide an external rotor brush DC motor, which has the rotor working as an inertia flywheel, thereby saving much material and processing cost and achieving high precision in dynamic balance.
To achieve these and other objects of the present invention, the external rotor brush DC motor comprises a shaft fixedly mounted on a bracket; a permanent magnet mounted on a middle part of the shaft and forming with the shaft a stator; a front wheel and a rear wheel mounted on the shaft with a respective axle bearing and spaded from the permanent magnet at front and rear sides, the front wheel having a belt pulley formed integral with the periphery thereof, the rear wheel having a through hole; a commutator provided at an outer side of the rear wheel for synchronous rotation with the rear wheel; a shell connected between the front wheel and the rear wheel for synchronous rotation; an iron core and a coil mounted in an inside wall of the shell and forming with the shell and the front wheel and the rear wheel a rotor, the coil having a lead wire inserted through the through hole of the rear wheel and electrically connected to the commutator; a cover affixed to the shaft and covered over the commutator; and a left-side electric brush and a right-side electric brush fixedly mounted inside the cover and respectively pressed on the commutator.